shell中的select用法
select也是循环的一种，它比较适合用在用户选择的情况下。 比如，我们有一个这样的需求，运行脚本后，让用户去选择数字，选择1，会运行w命令，选择2运行top命令，选择3运行free命令，选择4退出。脚本这样实现：[*] #!/bin/bash
[*] echo "Please chose a number, 1: run w, 2: run top, 3: run free, 4: quit"
[*] echo
[*] select command in w top free quit
[*] do
[*] case $command in
[*] w)
[*] w
[*] ;;
[*] top)
[*] top
[*] ;;
[*] free)
[*] free
[*] ;;
[*] quit)
[*] exit
[*] ;;
[*] *)
[*] echo "Please input a number:(1-4)."
[*] ;;
[*] esac
[*] done
执行结果如下：
sh select.sh
Please chose a number, 1: run w, 2: run top, 3: run free, 4: quit
1) w
2) top
3) free
4) quit
#? 1
16:03:40 up 32 days,2:42,1 user,load average: 0.01, 0.08, 0.08
USER TTY FROM LOGIN@> root pts/0 61.135.172.68 15:33 0.00s0.02s0.00s sh select.sh
#? 3
total used free shared buffers cached
Mem: 1020328 943736 76592 0 86840 263624
-/+ buffers/cache: 593272 427056
Swap: 2097144 44196 2052948
#?
我们发现，select会默认把序号对应的命令列出来，每次输入一个数字，则会执行相应的命令，命令执行完后并不会退出脚本。它还会继续让我们再次输如序号。序号前面的提示符，我们也是可以修改的，利用变量PS3即可，再次修改脚本如下：
[*] #!/bin/bash
[*] PS3="Please select a number: "
[*] echo "Please chose a number, 1: run w, 2: run top, 3: run free, 4: quit"
[*] echo
[*]
[*] select command in w top free quit
[*] do
[*] case $command in
[*] w)
[*] w
[*] ;;
[*] top)
[*] top
[*] ;;
[*] free)
[*] free
[*] ;;
[*] quit)
[*] exit
[*] ;;
[*] *)
[*] echo "Please input a number:(1-4)."
[*] esac
[*] done
如果想要脚本每次输入一个序号后就自动退出，则需要再次更改脚本如下：
[*] #!/bin/bash
[*] PS3="Please select a number: "
[*] echo "Please chose a number, 1: run w, 2: run top, 3: run free, 4: quit"
[*] echo
[*]
[*] select command in w top free quit
[*] do
[*] case $command in
[*] w)
[*] w;exit
[*] ;;
[*] top)
[*] top;exit
[*] ;;
[*] free)
[*] free;exit
[*] ;;
[*] quit)
[*] exit
[*] ;;
[*] *)
[*] echo "Please input a number:(1-4).";exit
[*] esac
[*] done
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